A mid-sized hydrogen-helium gas giant, Cyllene has an automated helium-3 refueling station, indicating that this remote system was once inhabited. Its distance from the mass relay and archaic design of the fuel station suggest that this system was mapped by someone who did not go through the relay but discovered it in independent FTL exploration. Cyllene is within the "frost line" of its parent star, where gas giants do not normally form.